The two other answers were probably typed at the same time mine was, but I was quicker to post it. Or, judging by how new LordMagikarp is, may have copied it and posted it, probably for points. Point grubbing, it's called. And I don't like it.

Go to weird house get the wing go to marvelous bridge in the center. you can catch cresselia there. On tips with shinies the masuda method chaining and running around aimlessly in the wild. Shiny cresselia you really want! so save before you battle her and keep soft ressetting until it is shiny!